Various seals are known for sealing shaft passages. Radial shaft sealing rings, slide-ring seals and the like are widespread, and their use areas are considerable. A common aspect of all seals is that they are subject to wear, and once the seal has lost its sealing function it must be replaced. Leaks occurring in such cases must be prevented, because a leak can cause major damage in many applications. Hence, the need exists for timely detection of an undesirable leak of a liquid or a gas so that the defective seal may be replaced.
A system for detecting leaks at a seal is known from DE 100 61 111 A1. The leak-detection system described therein comprises a depot for storing the leaked material and a sensor based on an optical principle. The sensor provides a signal when the optical properties of the depot have changed as a result of the depot being covered by the leaked liquid.
The size of the leak required to trigger signaling by the sensor depends on the positioning of the sensor in a space, namely on the orientation of the sensor in the space. Although the sensor's orientation can be pre-established at the time of installing a machine element into the machine unit, it cannot be ensured. The sensor will give a signal even for small, transient leaks that can occur when a foreign body passes through the sealing lip.